I program a lot in a dialect of Pascal called Pascal/D80, and due to dialectal features
and our own coding standards it is very common with nested comments in our source
code, sometimes in several levels. I have written a Pascal/D80 language mode for jEdit
which works quite well except that it cannot handle nested comments.

Basically, nested comments cannot be handled using only regular expressions. Depending
on how jEdit implements edit mode parsing it would either require recursive parsing
or a "level counter".